The invention relates to a process for the conversion of magnesium-bearing phosphate rock into phosphoric acid and a mixture of magnesium and calcium carbonates. Phosphate rock is mined as mineral rock containing a great variety of admixtures and is used as feedstock for the production of a magnitude of fertilizers.
Since phosphate rock is found in nature in different compositions it is necessary either to remove the admixtures and/or impurities from the process without disrupting the process or to convert them into usable products.
A method is known for processing magnesium-bearing phosphate rock with a content magnesium or magnesium compounds that is lower than 0.3% Mg or 0.5% MgO. This degree or contamination is sufficiently low to avoid any process disruptions. A German patent specification No. OS 25 31 519 describes a process in which phosphate rock with a magnesium content in excess of 0.3% is treated. The method described in German patent specification No. OS 25 31 519 enables the MgO content to be reduced for instance from 1.8% to a value of less than 0.5% by dissolving the magnesium compounds with the aid of sulphuric acid, thus obtaining phosphate rock that is largely free of magnesium and a filtrate containing dissolved magnesium sulphate. Said OS patent makes no mention of the use or disposal of the filtrate.